"Killers and Other Family" will be performed at the Rattlestick Playwrights Theater through Oct. 11.

‘KILLERS and Other Family” is far from perfect. Some of it defies common sense, the plot isn’t airtight, and the wild variations in tone can be trying.

Still, by the end of Lucy Thurber’s 2001 play, I was fidgeting in my seat, futilely fighting off the tension that emanated from the stage.

Discomforting an audience without resorting to shock tactics is no small feat, and “Killers” achieves it.

It all starts when Jeff (Dashiell Eaves) and best friend Danny (Shane McRae) barge into the apartment of Jeff’s sister, a graduate student named Elizabeth (Samantha Soule).

The scruffy men are on the lam, and their demeanor, flittering between friendly and threatening, is clearly disruptive. But Elizabeth’s reaction, as she goes from good-hostess politeness to thinly veiled hostility and back, is hard to figure out and even harder to empathize with.

Gradually we understand that the relationship between these three goes way back, when they were all growing up together in the boondocks. You see, Danny is a sociopath, and over the years the siblings, both attracted to and scared by him, have devised tricks to handle him.

Like Scheherazade in “Arabian Nights,” Elizabeth uses storytelling to keep violence at bay, but the complicit role she and Jeff play in their submission to Danny is never less than troubling.

When Elizabeth’s girlfriend Claire (Aya Cash) drops by on her lunch break, her presence throws the delicate balance out of whack. In a way Claire is us, the audience: After stumbling onto a bizarre game, she struggles to figure out what’s going on as her life — and by extension the show — turns into an urban version of “Deliverance.”

This is thorny stuff, and Thurber tries to juggle too many themes. But there’s also a sharp, ambitious intelligence at play here, and under the direction of Caitriona McLaughlin, the young cast handles it with aplomb.

Cash and Soule, in particular, fearlessly throw themselves into the show’s daunting physicality. As the actors take their bows, flushed and disheveled, you’re left feeling emotionally battered yet intensely alive.